Richard Sohn wrote:
> Cleared the ground for a brief period today. As far as the airplane is
> concerned, everything is good. CG seems to be right on the spot. Much
> better as it was 12 years ago at the first flight with the SOOB.
> Here is the reason why it was not a flight. A few days ago when I
> started high speed taxi, as soon as it picked up air speed, the engine
> started to sputter and almost cut out totally. This was at the same RPM
> as at a run up, where it does not do that. With a wiggly tail dragger as
> the Avid is, there was no way reading enough instrument for making a
> preliminary analysis. I recorded the instrument panel with a GoPro at
> 2sec intervals.
> Looking at the first pictures, the answer came up right away, increasing
> pressure under the cowl where the intake for the engine is located. Like
> the EGT shot up over 1600 just before the sputtering started. Since my
> radiator air is going to the outside of the cowling, there was no impact
> on cooling. Btw cooling is really good. At an OAT of 95F, oil and water
> stayed at around 170F no matter what I did.
>  
> For todays runs, I taped the inlet around the prop hub shut. Sure
> enough, the sputtering occurred at higher airspeed, and was not as
> total, however, EGT was still going to around 1600.
>  
> The conclusion is, I have to open the cowling exits a lot.

I don't get it.  The pressure under the cowl sounds like it would be a good thing, because it sounds like it is enough
to cause the engine to lean out.  If the cooling isn't a problem, why wouldn't you just enrichen the mixture to
accommodate the extra air and accept the increase in power?